Some fluid ejection devices, including, for example, inkjet printheads, have an orifice plate or orifice layer with nozzles or orifices through which fluid is ejected. Firing resistors in a firing chamber located below the orifice plate are selectively energized, thereby heating fluid in the chamber, causing some of the fluid in the chamber to boil and form a vapor bubble. The expanding vapor bubble pushes on the fluid, causing a drop of the fluid to be ejected from the nozzle.
Fluids to be ejected through the nozzles may include non-volatile components and volatile components. For example, in the case of an inkjet printhead an ink may be comprised of non-volatile dye or pigment components, non-volatile organic co-solvents, surfactants or buffers and a volatile component such as water. After a drop of fluid has been ejected, fluid entering the chamber refills the nozzle by capillary action. Between drop ejections, fluid remains in the nozzle and is subject to evaporation or diffusion of volatile components of the fluid out through the nozzle. As the volatile components of the remaining fluid evaporate from the open nozzle surface, non-volatile components are left behind. Such non-volatile components accumulate in the remaining volatile components over a period of several seconds and can increase the viscosity of fluid at the nozzle or form solid precipitates.
The increased viscosity fluid and/or the solid precipitates can reduce the performance of the fluid ejection device. For example, higher viscosity fluid or particulates in the nozzle can clog the nozzle, reduce the amount of fluid ejected through the nozzle, change the directional characteristics of drops ejected from the nozzle or otherwise alter the dynamics of drop ejection from the nozzle and degrading the performance of the fluid emitter. To maintain nozzle performance the ink can be periodically ejected or “spit” into a service station spittoon, to clear out evaporated ink from the nozzle. The use of a service station in this manner can reduce printer throughput speed and waste ink.